Gas composition for dry etching and dry etching method

ABSTRACT

A silicon oxide film or a silicon nitride film is selectively etched by using an etching gas composition including a hydrofluorocarbon that has an unsaturated bond in its molecule and is represented by CxHyFz, wherein x is an integer of from 3 to 5, and relationships y+z≤2x and y≤z are satisfied. Also, a silicon oxide film is etched with high selectivity relative to a silicon nitride film by controlling the ratio among the hydrofluorocarbon, oxygen, argon, etc., included in the hydrofluorocarbon-containing etching gas composition.

TECHNICAL FIELD

The present invention relates to a gas composition for dry etchingincluding a hydrofluorocarbon gas, and a dry etching method using thegas composition.

BACKGROUND ART

In present-day semiconductor devices, various active attempts, such asfine patterning and the use of novel materials, are being made toincrease speed and reduce power consumption. Fine patterning ofsemiconductor devices involves dry etching using fluorocarbon (referredto hereinafter also as “FC”) gas or hydrofluorocarbon (referred tohereinafter also as “HFC”) gas plasmas.

It is commonly known that, with FC gas plasmas having an unsaturatedbond or a cyclic structure including two or more carbon atoms, such asC₄F₈, C₄F₆, and C₅F₈, CFx radicals are deposited as a fluorocarbonpolymer on, for example, a silicon nitride film (referred to hereinafteralso as “SiN”), a polycrystalline silicon film (referred to hereinafteralso as “polysilicon” or “Poly-Si”), or a resist, and the deposit servesas a protection film, thus allowing a silicon oxide film (referred tohereinafter also as “SiOm” (wherein m represents a natural number)) tobe selectively etched relative to the aforementioned films.

It is also known that a silicon nitride film can be selectively etchedrelative to, for example, a silicon oxide film or a polysilicon film byusing a HFC gas including one carbon atom, such as CHF₃, CH₂F₂, andCH₃F.

Patent Literature 1 discloses a technique for etching, with highselectivity, a silicon nitride film relative to a silicon oxide film anda silicon film by using an unsaturated fluorohydrocarbon compoundrepresented by CxHyFz (wherein x=3, 4, or 5, y+z≤2x, and y>z) as theetching gas.

Patent Literature 2 discloses a technique for selectively etching asilicon-based material, such as a silicon oxide film or asilicon-containing low dielectric constant film (referred to hereinafteralso as “low-k film”), relative to a mask, such as silicon or a resist,with a C₄F₆ or C₅F₈ gas plasma. In the technique disclosed in thisPatent Literature, the C₄F₆ or C₅F₈ gas plasma produces a large amountof CF⁺ and radicals including three or more carbon atoms in the skeletonthereof (polymer radicals produced from CF₃CF═CFCF and CFCF═CF₂fragments). The technique disclosed in this Patent Literature is alsocharacteristic in that, although CF⁺ has a low etching efficiency,damage to the resist and silicon is minimal, and that the radicalsincluding three or more carbon atoms in the skeleton thereof form afluorocarbon polymer film having low density. The technique disclosed inthis Patent Literature is characteristic in that, by employing theaforementioned ions and radicals in a balanced manner, a silicon oxidefilm or a silicon-containing low dielectric constant film can beselectively etched without damaging the mask, such as the resist orsilicon. The Patent Literature also describes that it is also possibleto additionally achieve such effects as improved selectivity and lowboiling point by replacing, with hydrogen, a portion of the fluorineatoms in the fluorocarbon gas having two double bonds, such as C₄F₆ orC₅F₈.

Patent Literature 3 discloses, in relation to the etching of holestructures patterned by a resist in a multilayer structure including asilicon oxide film and a silicon nitride film, a technique that allowsselective etching of a silicon oxide film and a silicon nitride filmrelative to a resist by using a HFC-based gas plasma represented byCaHbFc (wherein a is from 3 to 5, b is from 1 to 2, and c is from 3 to10). The decomposition of CaHbFc (wherein a is from 3 to 5, b is from 1to 2, and c is from 3 to 10) in a plasma produces CF radicalsoriginating from fluorocarbons and CH radicals originating fromhydrocarbons. The CF radicals etch the silicon oxide film withoutreacting with the silicon nitride film. The CH radicals are smaller thanthe CF radicals, and thus, deeply penetrate the contact hole and etchthe silicon nitride film.

CITATION LIST Patent Literature

Patent Literature 1: US 2014306146 A1

Patent Literature 2: JP 2011-86966A

Patent Literature 3: JP 2008-300616A

SUMMARY OF INVENTION

Etching using C₄F₈, C₄F₆, C₅F₈, or the like has heretofore been employedas a method for selectively etching a silicon oxide film relative to aresist, a silicon film (crystalline silicon, amorphous silicon, orpolysilicon), a silicon nitride film, a carbon-containing silicon-basedfilm (e.g., SiC, SiOC, SiCN, SiOCN), or the like. Further, selectivitytoward silicon oxide film is improved by adding H₂, CO, or a HFC gas,such as CH₂F₂ or CH₃F, to the aforementioned FC gases. Also, by etchingusing a HFC gas, a silicon nitride film is selectively etched relativeto a resist, a silicon film (crystalline silicon, amorphous silicon,polysilicon), a carbon-containing silicon-based film, or the like.

In order to selectively etch each of the silicon oxide film and thesilicon nitride film relative to a resist, a silicon film (crystallinesilicon, amorphous silicon, polysilicon), or a carbon-containingsilicon-based film, it is necessary to change the types of FC gases andHFC gases in accordance with the respective types of films.

Also, in recent years, low dielectric constant materials, such as SiOC,are used for carbon-containing silicon-based films in order to reduceparasitic capacitance that increases with the miniaturization ofsemiconductor devices. It is, however, difficult to selectively etchsilicon oxide films and silicon nitride films relative to low dielectricconstant materials with existing FC gases and/or HFC gases. Actualdevice production involves problems such as that the low dielectricconstant film is damaged at the time of dry etching (the compositionand/or structure of the film are/is changed by the penetration of ionsor by ultraviolet rays generated by plasma, and thus, electriccharacteristics such as permittivity are changed).

As a result of diligent research to solve the aforementioned problems,Inventors have found that an etching gas composition including aspecific hydrofluorocarbon is effective, thus arriving at the presentinvention.

More specifically, by using a HFC gas that has an unsaturated bond inits molecule and is represented by CxHyFz, wherein x is an integer offrom 3 to 5 and relationships y+z≤2x and y≤z are satisfied, it ispossible to selectively etch a silicon oxide film, or a silicon oxidefilm and a silicon nitride film, relative to a carbon film asrepresented by amorphous carbon (referred to hereinafter also as “ACL”),a silicon film as represented by Poly-Si, a silicon oxynitride film(referred to hereinafter also as “SiON”), or a carbon-containingsilicon-based film as represented by SiC, SiOC, SiCN, or SiOCN.

The present invention provides the following aspects.

Aspect 1: A gas composition for dry etching, including a HFC gas thathas an unsaturated bond in its molecule and is represented by CxHyFz,wherein x is an integer of from 3 to 5, and relationships y+z≤2x and y≤zare satisfied.

Aspect 2: The gas composition for dry etching as set forth in Aspect 1,wherein the HFC gas includes 1,1,4,4-tetrafluoro-1,3-butadiene.

Aspect 3: The gas composition for dry etching as set forth in Aspect 2,wherein the content of 1,1,4,4-tetrafluoro-1,3-butadiene in the HFC isfrom 1 to 100 vol %.

Aspect 4: The gas composition for dry etching as set forth in Aspect 2or 3, wherein the gas composition for dry etching includes, in additionto 1,1,4,4-tetrafluoro-1,3-butadiene, at least one compound selectedfrom the group of oxygen-atom-containing compounds consisting of O₂, O₃,CO, CO₂, NO, NO₂, SO₂, and SO₃.

Aspect 5: The gas composition for dry etching as set forth in Aspect 2,wherein the gas composition for dry etching includes, in addition to1,1,4,4-tetrafluoro-1,3-butadiene, at least one compound selected fromthe group of inert gases consisting of N₂, He, Ar, Ne, and Xe.

Aspect 6: A dry etching method involving a selective etching stepwherein a multilayer structure including

-   -   (a1) a carbon-containing silicon-based film, (a2) a crystalline        silicon film, (a3) an amorphous silicon film, (a4) a        polycrystalline silicon film (polysilicon film), (a5) a silicon        oxynitride film, or (a6) an amorphous carbon film, and    -   (b1) a silicon oxide film or (b2) a silicon nitride film        is subjected to etching by using the gas composition for dry        etching as set forth in any one of Aspects 1 to 5, and thus        selectively etching the silicon oxide film (b1) or the silicon        nitride film (b2).

Aspect 7: The dry etching method as set forth in Aspect 6, whereinetching with the gas composition for dry etching is performed under aplasma condition in which the silicon oxide film (b1) and the siliconnitride film (b2) can be etched simultaneously.

Aspect 8: The dry etching method as set forth in Aspect 6, whereinetching of the silicon oxide film (b1) is performed selectively relativeto the silicon nitride film (b2).

Aspect 9: The dry etching method as set forth in any one of Aspects 6 to8, wherein etching is performed by turning the etching gas compositioninto plasma so that ions having 3 to 5 carbon atoms are produced.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1(a) and 1(b) are diagrams of steps sequentially illustrating amethod for performing dry etching according to the invention.

FIGS. 2(a) to 2(c) are diagrams of steps sequentially illustratinganother method for performing dry etching according to the invention.

FIGS. 3(a) to 3(c) are cross-sectional views illustrating multilayerstructures of objects to be etched by dry etching methods of theinvention, and diagrams illustrating other methods for performing dryetching according to the invention.

DESCRIPTION OF EMBODIMENTS

A gas composition for dry etching according to the present invention anda dry etching method using the same are described in detail below. Thescope of the invention is not limited to the scope described below, andvarious modifications can be made within a scope that does not departfrom the gist of the invention.

A gas composition for dry etching of the invention includes a HFC gasthat is represented by formula (I) below. In the formula, x is aninteger of from 3 to 5, and y and z are also positive integers andsatisfy the relationships y+z≤2x and y≤z.

CxHyFz  (1)

The HFC gas represented by formula (1) includes an unsaturated bond inits molecule. The unsaturated bond is C═C and/or C≡C. There is at leastone unsaturated bond depending on the number of carbon atoms in the HFCgas represented by formula (1).

In the invention, it is possible to use one type, or two or more types,of the HFC gas(es) represented by formula (1). The HFC gas representedby formula (1) may have a chain structure, or may have a cyclicstructure. In the case where the HFC gas represented by formula (1) hasa chain structure, the chain structure may be a straight chain or may bea branched chain.

In the case where the HFC gas represented by formula (1) has threecarbon atoms, examples of preferable basic skeletons of the HFC gasinclude the following (3a) to (3d).

C═C—C  (3a)

C≡C—C  (3b)

C═C═C  (3c)

—C═C—C— (representing a 3-membered cyclic structure)  (3d)

In the case where the HFC gas represented by formula (1) has four carbonatoms, examples of preferable basic skeletons of the HFC gas include thefollowing (4a) to (4o).

C═C—C—C  (4a)

C—C═C—C  (4b)

C—C—(C)═C (below, “( )” represents a branched structure)  (4c)

C≡C—C—C  (4d)

C—C≡C—C  (4e)

C═C—C═C  (4f)

C═C═C—C  (4g)

—C—C═C—C— (representing a 4-membered cyclic structure)  (4h)

—C═C—(C)—C— (representing a 3-membered cyclic structure)  (4i)

—C—C—(C)—C═ (representing a 3-membered cyclic structure)  (4j)

—C—C═(C)—C— (representing a 3-membered cyclic structure)  (4k)

C≡C—C═C  (4l)

—C═C—C═C— (representing a 4-membered cyclic structure)  (4m)

—C—C═(C)—C═ (representing a 3-membered cyclic structure)  (4n)

C≡C—C≡C  (4o)

In the case where the HFC gas represented by formula (1) has five carbonatoms, examples of preferable basic skeletons of the HFC gas include thefollowing (5a) to (5as).

C═C—C—C—C  (5a)

C—C═C—C—C  (5b)

C—C—C—(C)═C  (5c)

C—C═C—(C)—C  (5d)

C≡C—C—C—C  (5e)

C—C≡C—C—C  (5f)

C═C—C═C—C  (5g)

C═C═C—C—C  (5h)

C═C—C—C═C  (5i)

C═C—(C)—C═C  (5j)

C—C—(C)—C≡C  (5k)

C—C═C═C—C  (5l)

C—C—(C)═C═C  (5m)

—C—C═C—C—C— (representing a 5-membered cyclic structure)  (5n)

—C—C—(C)—C═C— (representing a 4-membered cyclic structure)  (5o)

—C═C—(C)—C—C— (representing a 4-membered cyclic structure)  (5p)

—C—C═(C)—C—C— (representing a 4-membered cyclic structure)  (5q)

—C—(C)—C—(C)═C— (representing a 3-membered cyclic structure)  (5r)

—C—(C)═C—(C)—C— (representing a 3-membered cyclic structure)  (5s)

—C═(C)—C—(C)—C— (representing a 3-membered cyclic structure)  (5t)

—C—C—(C)(C)—C═ (representing a 3-membered cyclic structure)  (5u)

—C—C—(C—C)═C— (representing a 3-membered cyclic structure)  (5v)

—C—C—(C—C)—C═ (representing a 3-membered cyclic structure)  (5w)

—C—C═(C—C)—C— (representing a 3-membered cyclic structure)  (5x)

—C—C—(C═C)—C— (representing a 3-membered cyclic structure)  (5y)

C≡C—C═C—C  (5z)

C═C═C═C—C  (5aa)

C═C—C—C≡C  (5ab)

C═C—(C)—C≡C  (5ac)

C═C—C≡C—C  (5ad)

C═C—C═C═C  (5ae)

—C—C═C—C═C— (representing a 5-membered cyclic structure)  (5af)

—C═C—(C)—C═C— (representing a 4-membered cyclic structure)  (5ag)

—C—C═(C)—C═C— (representing a 4-membered cyclic structure)  (5ah)

—C═(C)—C═(C)—C— (representing a 3-membered cyclic structure)  (5ai)

—C═(C)—C—(C)═C— (representing a 3-membered cyclic structure)  (5aj)

—C═C—(C═C)—C— (representing a 3-membered cyclic structure)  (5ak)

—C—C═(C—C)—C═ (representing a 3-membered cyclic structure)  (5al)

—C—C—(C═C)—C═ (representing a 3-membered cyclic structure)  (5am)

—C—C—(C≡C)—C— (representing a 3-membered cyclic structure)  (5an)

C≡C—C—C≡C  (5ao)

C—C≡C—C≡C  (5ap)

C═C═C—C≡C  (5aq)

—C—C—(C≡C)—C═ (representing a 3-membered cyclic structure)  (5ar)

—C═C—(C≡C)—C— (representing a 3-membered cyclic structure)  (5as)

In the case where the HFC gas used in the invention is represented bythe aforementioned formula (3a), it is preferable that the number offluorine atoms included therein is from 3 to 5. In the case where theHFC gas is represented by one of the aforementioned formulas (3b) to(3d), it is preferable that the number of fluorine atoms is from 2 to 3.

In the case where the HFC gas used in the invention is represented byone of the aforementioned formulas (4a) to (4c), it is preferable thatthe number of fluorine atoms included therein is from 4 to 7. In thecase where the HFC gas is represented by one of the aforementionedformulas (4d) to (4k), it is preferable that the number of fluorineatoms is from 3 to 5. In the case where the HFC gas is represented byone of the aforementioned formulas (4l) to (4n), it is preferable thatthe number of fluorine atoms is from 2 to 3. In the case where the HFCgas is represented by the aforementioned formula (4o), the number offluorine atoms is 1.

In the case where the HFC gas used in the invention is represented byone of the aforementioned formulas (5a) to (5d), it is preferable thatthe number of fluorine atoms included therein is from 5 to 9. In thecase where the HFC gas is represented by one of the aforementionedformulas (5e) to (5y), it is preferable that the number of fluorineatoms is from 4 to 8. In the case where the HFC gas is represented byone of the aforementioned formulas (5z) to (5an), it is preferable thatthe number of fluorine atoms is from 3 to 5. In the case where the HFCgas is represented by one of the aforementioned formulas (5ao) to (5as),it is preferable that the number of fluorine atoms is from 2 to 3.

HFC gases that may be preferably used in the invention are representedby one of the aforementioned formulas (4a) to (4o); among the above,gases represented by formula (4f) are further preferred. It ispreferable that, in the HFC gases represented by formula (4f), thenumber of fluorine atoms is from 3 to 5, and more preferably, the numberof fluorine atoms is 4. Particularly, the HFC gas represented by formula(4t) is preferably 1,1,4,4-tetrafluoro-1,3-butadiene. More specifically,in the invention, by using a gas plasma of1,1,4,4-tetrafluoro-1,3-butadiene, wherein a portion of the fluorineatoms in C₄F₆ is replace by hydrogen, it is possible to etch a siliconoxide film and/or a silicon nitride film with high selectivity relativeto mask materials, such as ACL, Poly-Si, and SiON, and also relative toSiOC, which is a silicon-containing low-k material.

Many of the HFC gases represented by the various structures shown aboveare known substances, and can be produced and obtained by known methods.For example, such gases can be produced and obtained by methodsdescribed in the Journal of Fluorine Chemistry (1997), vol. 82 (2), pp.171-174. Alternatively, commercially available products may be usedas-is, or after purification as desired.

The etching method of the invention is a dry etching method usingplasma, and is performed by using a gas composition for dry etchingincluding one type, or two or more types, of HFC gas(es) represented byformula (1). Particularly, it is preferable to use only1,1,4,4-tetrafluoro-1,3-butadiene as the HFC gas represented by formula(1).

In the dry-etching gas composition used for etching, it is preferablethat the content of 1,1,4,4-tetrafluoro-1,3-butadiene in the HFC gas isfrom 1 to 100 vol %. Particularly, the purity of1,1,4,4-tetrafluoro-1,3-butadiene can be 90 vol % or higher, and it ispreferable that the purity is 99 vol % or higher, and more preferably99.999 vol % or higher. The effect of the invention is further enhancedwhen the purity is within the aforementioned range.

The etching gas composition used in the plasma etching method of theinvention preferably includes, in addition to HFC gas(es) represented byformula (1), at least one compound selected from the group ofoxygen-atom-containing compounds consisting of O₂, O₃, CO, CO₂, NO, NO₂,SO₂, and SO₃. Particularly among the group of oxygen-atom-containingcompounds, it is more preferable to use O₂. The percentage of the groupof oxygen-atom-containing compounds within the etching gas compositionis preferably from 10 vol % to 80 vol %, more preferably from 10 vol %to 60 vol %.

Further, it is preferable that the etching gas composition includes theHFC gas(es) represented by formula (1), and at least one compoundselected from the group of inert gases consisting of N₂, He, Ar, Ne, andXe, in addition to, or in place of, the aforementionedoxygen-atom-containing compound(s). Particularly among the group ofinert gases, it is more preferable to use Ar.

The percentage of the HFC gas(es) represented by formula (I) mixed inthe etching gas composition is preferably within the range from 1 to 100vol %. The percentage of gas(es) selected from the group ofoxygen-atom-containing compounds consisting of O₂, O₃, CO, CO₂, NO, NO₂,SO₂, and SO₃ is preferably within the range from 1 to 80 vol %. Thepercentage of gas(es) selected from the group of inert gases consistingof N₂, He, Ar, Ne, and Xe is preferably within the range from 1 to 80vol %. Particularly in the case where O₂ is used, the effect of theinvention is further enhanced by mixing the HFC gas(es) represented byformula (1) at a percentage (by volume) of from 5 to 50 vol % and mixingO₂ at a percentage of from 10 to 80 vol %.

Plasma etching of the invention is preferably performed within apressure range from 0.01 to 100 Pa, more preferably within a range from0.1 to 10 Pa.

Any plasma etching device known in the present technical field may beused without particular limitation. For example, it is possible to use ahelicon wave-type, a high-frequency induction-type, a parallelplate-type, a magnetron-type, or a microwave-type device.

The plasma density is not particularly limited, but it is preferable toperform etching in a high-density plasma atmosphere of 10⁸ ions/cm³ orhigher, more preferably from 10⁸ to 10¹³ ions/cm³.

An example of an object subjected to plasma etching is a multilayerstructure including: (a1) a carbon-containing silicon-based film, (a2) acrystalline silicon film, (a3) an amorphous silicon film, (a4) apolycrystalline silicon film (polysilicon film), (a5) a siliconoxynitride film, or (a6) an amorphous carbon film; and (b1) a siliconoxide film or (b2) a silicon nitride film. In this type of multilayerstructure, the film (b1) or (b2) (referred to hereinafter as “firstlayer 11”) can serve as the etching surface as illustrated in FIG. 1(a),or the film of one of (a1) to (a6) (referred to hereinafter as “secondlayer 12”) can serve as the etching surface as illustrated in FIG. 2(a).

In the embodiment illustrated in FIG. 1(a), a mask 13 having apredetermined pattern formed thereon is arranged on a surface of a firstlayer 11 of a multilayer structure 10, and dry etching is performed fromthe mask 13 side. The HFC gas represented by formula (1) selectivelyetches the first layer 11 as illustrated in FIG. 1(b), and the etchingprogresses to a surface of a second layer 12 located beneath the firstlayer 11. The HFC gas represented by formula (1) does not etch thesecond layer 12, and thus, the etching stops when the surface of thesecond layer 12 is exposed.

In the embodiment illustrated in FIG. 2(a), a mask 13 having apredetermined pattern formed thereon is arranged on a surface of thesecond layer 12 of the multilayer structure 10, and the layer 12 isetched as illustrated in FIG. 2(b) by using a gas capable of selectivelyetching the second layer 12. Then, as illustrated in FIG. 2(c), the HFCgas represented by formula (1) is used to selectively etch the firstlayer 11. At this time, the second layer 12 is not etched.

In both the embodiments illustrated in FIGS. 1 and 2, etching can beperformed under a plasma condition in which the silicon oxide film (b1)and the silicon nitride film (b2) can be etched simultaneously byappropriately controlling the plasma etching condition. Thissimultaneous etching is advantageous in the case where the first layer11 consists of a multilayer structure including an upper layer 11 a madeof a silicon oxide film or a silicon nitride film and a lower layer 11 bmade of a silicon nitride film or a silicon oxide film, as illustratedin FIG. 3(a). Particularly in the case where the multilayer structure 10further includes a second layer 12 arranged below the lower layer 11 bas illustrated in FIG. 3(b), the HFC gas represented by formula (1)etches the upper layer 11 a and the lower layer 11 b simultaneously, butthe lowermost second layer 12 is not etched. That is, the etching stopson the surface of the lowermost second layer 12. An example of a plasmacondition in which the silicon oxide film (b1) and the silicon nitridefilm (b2) can be etched simultaneously is a condition where the etchinggas composition contains 5 to 40 vol % of1,1,4,4-tetrafluoro-1,3-butadiene, 15 to 80 vol % of and 0 to 75 vol %of Ar, and the ratio of 1,1,4,4-tetrafluoro-1,3-butadiene to O₂ isselected discretionarily from 1:X (wherein 3≤X). The conditions for thepressure and RF power can be set such that a silicon oxide film and asilicon nitride film can be etched simultaneously in the aforementionedgas composition; for example, the pressure may be 10 Pa, and the RFpower may be 300 W.

In contrast to the aforementioned simultaneous etching, in an embodimentwhere the first layer 11 of the multilayer structure 10 is constitutedby an upper layer 11 a made of a silicon oxide film and a lower layer 11b made of a silicon nitride film and the first layer 11 is arrangedbelow the second layer as illustrated in FIG. 3(c), etching of thesilicon oxide film (b1) may be performed selectively relative to thesilicon nitride film (b2). With this selective etching, the upper layer11 a made of a silicon oxide film is etched whereas the lower layer 11 bmade of a silicon nitride film is not, and the etching stops at a stagewhere the surface of the lower layer 11 b is exposed. An example of aplasma condition in which this kind of etching is possible is acondition where the etching gas composition contains 5 to 50 vol % of1,1,4,4-tetrafluoro-1,3-butadiene, 10 to 75 vol % of O₂, and 0 to 85 vol% of Ar, and the ratio of 1,1,4,4-tetrafluoro-1,3-butadiene to O₂ isselected discretionarily from 1:X (wherein 0<X<3). The conditions forthe pressure and RF power can be set such that a silicon oxide film canbe etched but a silicon nitride film is hard to etch in theaforementioned gas composition; for example, the pressure may be 10 Pa,and the RF power may be 300 W.

In all of the embodiments illustrated in FIGS. 1 to 3, it is preferableto use, for etching, ions having 3 to 5 carbon atoms, which are producedby turning the etching gas composition into plasma, because highlyselective etching can be performed. For example, when1,1,4,4-tetrafluoro-1,3-butadiene is employed as the HFC gas, a plasmacondition capable of producing such ions is a condition where1,1,4,4-tetrafluoro-1,3-butadiene ranges from 5 to 50 vol %, O₂ rangesfrom 10 to 80 vol %, and Ar ranges from 0 to 85 vol %. The conditionsfor the pressure and RF power can be set such that ions having 3 to 5carbon atoms can be produced with the aforementioned gas composition;for example, the pressure may be 10 Pa, and the RF power may be 300 W.

EXAMPLES

The present invention is described in further detail below according toExamples and Comparative Examples. The invention, however, is notlimited thereto.

In the present Examples, a parallel plate-type capacitively coupledplasma etching device was used for the plasma etching device. Thesilicon oxide film (SiOm) (m represents a natural number) used wasobtained by depositing 1000 nm of a SiO₂ film on a silicon wafer byplasma CVD. The silicon nitride film (SiN) used was obtained bydepositing 300 nm of a SiN film on a silicon wafer by thermal CVD. Thepolysilicon film used was obtained by depositing, by plasma CVD, 300 nmof a Poly-Si film on a laminate obtained by depositing 100 nm of a SiO₂film on a silicon wafer. The amorphous carbon film used was obtained bydepositing 100 nm of ACL on a silicon wafer by plasma CVD. Thecarbon-containing silicon film used was obtained by depositing 500 nm ofBlack Diamond 3 (referred to hereinafter as “BD-3”), which is a type ofSiOC, on a silicon wafer.

The etching rate measurement in plasma etching was calculated accordingto the following equation.

Etching rate (nm/min)=[Sample film thickness before etching (nm)−Samplefilm

thickness after etching (nm)]/Etching time (min).

The film thickness of a sample was measured with an optical interferencefilm-thickness measurement device.

Examples 1 to 5

A plasma was generated using a composition of 14 vol %1,1,4,4-tetrafluoro-1,3-butadiene, 50 vol % O₂, and 36 vol % Ar under apressure condition of 10 Pa and RE power condition of 300 W, andrespective samples of a SiO₂ film, a SiN film, a Poly-Si film, an ACLfilm, and a BD-3 film were each subjected to etching. The1,1,4,4-tetrafluoro-1,3-butadiene employed was produced according to themethod described in the Journal of American Chemical Society (1961),vol. 83, pp. 382-5. The etching rate of each sample was as follows: SiO₂film: 18.3 nm/min; SiN film: 0 nm/min; Poly-Si film: 0 nm/min; ACL film:0 nm/min; BD-3: 0 nm/min. The selectivity ratio of the SiO₂ filmrelative to the other types of films, as calculated by the followingequation using the etching rates of the respective samples, wasinfinity. In the present Examples, it was verified that ions having 3 to5 carbon atoms were produced during plasma etching. This was verified byintroducing a quadrupole mass spectrometer in a treatment chamber inwhich the plasma was generated, and subjecting the ions in the plasma tomass spectrometry.

Selectivity ratio=Etching rate of film for which selectivity ratio is tobe found/Etching rate of another film.

Examples 6 to 10

A plasma was generated using a composition of 13 vol %1,1,4,4-tetrafluoro-1,3-butadiene, 53 vol % O₂, and 34 vol % Ar under apressure condition of 10 Pa and RF power condition of 300 W, andrespective samples of a SiO₂ film, a SiN film, a Poly-Si film, an ACLfilm, and a BD-3 film were each subjected to etching. The etching rateof each sample was as follows: SiO₂ film: 30.6 nm/min; SiN film: 17.4nm/min; Poly-Si film: 1.1 nm/min; ACL film: 0 nm/min; BD-3: 0 nm/min.The selectivity ratio of the SiO₂ film relative to the other types offilms was as follows: relative to SiN film: 1.8; relative to Poly-Sifilm: 27.8; relative to ACL film: infinity; relative to BD-3 film:infinity. The selectivity ratio of the SiN film relative to the othertypes of films was as follows: relative to SiO₂ film: 0.6; relative toPoly-Si: 15.8; relative to ACL film: infinity; relative to BD-3 film:infinity. In the present Examples, it was verified that ions having 3 to5 carbon atoms were produced during plasma etching.

Comparative Examples 1 to 5

These Comparative Examples are examples in which C₄F₆ was used insteadof 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gas used inthe Examples. A plasma was generated using a composition of 20 vol %C₄F₆, 30 vol % O₂, and 50 vol % Ar under a pressure condition of 10 Paand RF power condition of 300 W, and respective samples of a SiO₂ film,a SiN film, a Poly-Si film, an ACL film, and a BD-3 film were eachsubjected to etching. The etching rate of each sample was as follows:SiO₂ 63.6 nm/min; SiN film: 12.4 nm/min; Poly-Si film: 5.9 μm/min; ACLfilm: 0 nm/min; BD-3: 29.7 nm/min. The selectivity ratio of the SiO₂film relative to the other types of films was as follows: relative toSiN film: 5.1; relative to Poly-Si film: 10.8; relative to ACL film:infinity; relative to BD-3 film: 2.1. The selectivity ratio of the SiNfilm relative to the other types of films was as follows: relative toSiO₂ film: 0.2; relative to Poly-Si: 2.1; relative to ACL film:infinity; relative to BD-3 film: 0.4.

Comparative Examples 6 to 10

These Comparative Examples are also examples in which C₄F₆ was usedinstead of 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gasused in the Examples. A plasma was generated using a composition of 14vol % C₄F₆, 50 vol % 02, and 36 vol % Ar under a pressure condition of10 Pa and RF power condition of 300 W, and film samples were eachsubjected to etching. The etching rate of each sample was as follows:SiO₂ film: 45.0 nm/min; SiN film: 48.5 nm min; Poly-Si film: 31.0nm/min; ACL film: 58.1 nm/min; BD-3: 92.0 nm/min. The selectivity ratioof the SiO₂ film relative to the other types of films was as follows:relative to SiN film: 0.9; relative to Poly-Si film: 1.5; relative toACL film: 0.8; relative to BD-3 film: 0.5. The selectivity ratio of theSiN film relative to the other types of films was as follows: relativeto SiO₂ film: 1.1; relative to Poly-Si: 1.6; relative to ACL film: 0.8;relative to BD-3 film: 0.5.

Comparative Examples 10 to 15

These Comparative Examples are also examples in which C₄F₆ was usedinstead of 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gasused in the Examples. A plasma was generated using a composition of 13vol % C₄F₆, 53 vol % O₂, and 34 vol % Ar under a pressure condition of10 Pa and RF power condition of 300 W, and respective samples of a SiO₂film, a SiN film, a Poly-Si film, an ACL film, and a BD-3 film were eachsubjected to etching. The etching rate of each sample was as follows:SiO₂ film: 43.9 nm/min; SiN film: 45.0 nm/min; Poly-Si film: 26.7nm/min; ACL film: 68.3 nm/min; BD-3: 90.3 nm/min. The selectivity ratioof the SiO₂ film relative to the other types of films was as follows:relative to SiN film: 1.0; relative to Poly-Si film: 1.6; relative toACL film: 0.6; relative to BD-3 film: 0.5. The selectivity ratio of theSiN film relative to the other types of films was as follows: relativeto SiO₂ film: 1.0; relative to Poly-Si: 1.7; relative to ACL film: 0.7;relative to BD-3 film: 0.5.

Comparative Examples 16 to 20

These Comparative Examples are examples in which CH₃F was used insteadof 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gas used inthe Examples. A plasma was generated using a composition of 29 vol %CH₃F, 0 vol % O₂, and 71 vol % Ar under a pressure condition of 10 Paand RF power condition of 300 W, and respective samples of a SiO₂ film,a SiN film, a Poly-Si film, an ACL film, and a BD-3 film were eachsubjected to etching. The result was that etching did not proceed in anyof the samples.

Comparative Examples 21 to 25

These Comparative Examples are also examples in which CH₃F was usedinstead of 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gasused in the Examples. A plasma was generated using a composition of 27vol % CH₃F, 6 vol % O₂, and 67 vol % Ar under a pressure condition of 10Pa and RE power condition of 300 W, and respective samples of a SiO₂film, a SiN film, a Poly-Si film, an ACL film, and a BD-3 film were eachsubjected to etching. The etching rate of each sample was as follows:SiO₂ film: 17.7 nm/min; SiN film: 123.4 nm/min; Poly-Si an: 6.8 nm/min;ACL an: 10.0 nm/min; BD-3: 24.6 nm/min. The selectivity ratio of theSiO₂ film relative to the other types of films was as follows: relativeto SiN film: 0.1; relative to Poly-Si film: 2.6; relative to ACL film:1.8; relative to BD-3 film: 0.7. The selectivity ratio of the SiN filmrelative to the other types of films was as follows: relative to SiO₂film: 7.0; relative to Poly-Si: 18.1; relative to ACL film: 12.3;relative to BD-3 film: 5.0.

Comparative Examples 21 to 30

These Comparative Examples are also examples in which CH₃F was usedinstead of 1,1,4,4-tetrafluoro-1,3-butadiene, which was the etching gasused in the Examples. A plasma was generated using a composition of 25vol % CH₃F, 13 vol % 02, and 62 vol % Ar under a pressure condition of10 Pa and RF power condition of 300 W, and respective samples of a SiO₂film, a SiN film, a Poly-Si film, an ACL film, and a BD-3 film were eachsubjected to etching. The etching rate of each sample was as follows:SiO₂ film: 9.9 nm/min; SiO₂ film: 91.5 nm/min; Poly-Si film: 6.6 nm/min;ACL film: 84.7 nm/min; BD-3: 27.0 nm/min. The selectivity ratio of theSiO₂ film relative to the other types of films was as follows: relativeto SiN film: 0.1; relative to Poly-Si film: 1.5; relative to ACL film:0.1; relative to BD-3 film: 0:4. The selectivity ratio of the SiN filmrelative to the other types of films was as follows: relative to SiO₂film: 9.2; relative to Poly-Si: 13.9; relative to ACL film: 1:1;relative to BD-3 film: 3.4.

The etching results are shown in the table below

TABLE 1 Etching Etching Etching Etching gas O₂ Ar rate SiO₂ film SiNfilm condition sample (vol %) (vol %) (vol %) (nm/min) selectivityselectivity Example 1 Etching gas: SiO₂ film 14 50 36 18.3 — — Example 2C₄H₂F₄ SiN film 14 50 36 0 ∞ — Example 3 Pressure: 10 Pa Poly-Si film 1450 36 0 ∞ — Example 4 RF power: 300 W ACL film 14 50 36 0 ∞ — Example 5BD-3 film 14 50 36 0 ∞ — Example 6 SiO₂ film 13 53 34 30.6 — 0.6 Example7 SiN film 13 53 34 17.4 1.8 — Example 8 Poly-Si film 13 53 34 1.1 27.8 15.8  Example 9 ACL film 13 53 34 0 ∞ ∞ Example 10 BD-3 film 13 53 34 0∞ ∞ Comp. Example 1 Etching gas: C₄F₆ SiO₂ film 20 30 50 63.6 — 0.2Comp. Example 2 Pressure: 10 Pa SiN film 20 30 50 12.4 5.1 — Comp.Example 3 RF Power: 300 W Poly-Si film 20 30 50 5.9 10.8  2.1 Comp.Example 4 ACL film 20 30 50 0 ∞ ∞ Comp. Example 5 BD-3 film 20 30 5029.7 2.1 0.4 Comp. Example 6 SiO₂ film 14 50 36 45.0 — 1.1 Comp. Example7 SiN film 14 50 36 48.4 0.9 — Comp. Example 8 Poly-Si film 14 50 3631.0 1.5 1.6 Comp. Example 9 ACL film 14 50 36 58.1 0.8 0.8 Comp.Example BD-3 film 14 50 36 92.0 0.5 0.5 Comp. Example SiO₂ film 13 53 3443.9 — 1.0 Comp. Example SiN film 13 53 34 45.0 1.0 — Comp. ExamplePoly-Si film 13 53 34 26.7 1.6 1.7 Comp. Example ACL film 13 53 34 68.30.6 0.7 Comp. Example BD-3 film 13 53 34 90.3 0.5 0.5 Comp. ExampleEtching gas: SiO₂ film 29 0 71 0 — — Comp. Example CH₃F SiN film 29 0 710 — — Comp. Example Pressure: 10 Pa Poly-Si film 29 0 71 0 — — Comp.Example RF power: 300 W ACL film 29 0 71 0 — — Comp. Example BD-3 film29 0 71 0 — — Comp. Example SiO₂ film 27 6 67 17.7 — 7.0 Comp. ExampleSiN film 27 6 67 123.4 0.1 — Comp. Example Poly-Si film 27 6 67 6.8 2.618.1  Comp. Example ACL film 27 6 67 10.0 1.8 12.3  Comp. Example BD-3film 27 6 67 24.6 0.7 5.0 Comp. Example SiO₂ film 25 13 62 9.9 — 9.2Comp. Example SiN film 25 13 62 91.5 0.1 — Comp. Example Poly-Si film 2513 62 6.6 1.5 13.9  Comp. Example ACL film 25 13 62 84.7 0.1 1.1 Comp.Example BD-3 film 25 13 62 27.0 0.4 3.4

Examples 1 to 5 show that an etching gas composition including1,1,4,4-tetrafluoro-1,3-butadiene is capable of etching a SiO₂ film withhigh selectivity relative to other films.

Examples 6 to 10 show that, by adjusting the flow amount of 0, in anetching gas composition including 1,1,4,4-tetrafluoro-1,3-butadiene,both SiO₂ and SiN films can be etched with high selectivity relative toother films.

A comparison between the results of the present Examples and the resultsof Comparative Examples 1 to 30 shows that etching can be performed withgreater selectivity by using an etching gas composition including1,1,4,4-tetrafluoro-1,3-butadiene, compared to existing etching gases.

INDUSTRIAL APPLICABILITY

With the etching gas composition including a HFC gas represented byformula (1), it is possible to etch, with high selectivity, a siliconoxide film and/or a silicon nitride film relative to other films. Thus,in a multilayer structure including, for example, a silicon oxide film,a silicon nitride film, and/or a low-k film and having a pattern formedwith a mask material, such as Poly-Si, ACL, or SiON, this gascomposition can be employed for fine patterning for selectively etchingthe silicon oxide film and/or the silicon nitride film.

Plasma etching employing the hydrofluorocarbon gas composition of theinvention solves conventional problems and issues, and has the followingadvantages.

(1) A silicon oxide film or a silicon nitride film is etched with highselectivity relative to a carbon-containing silicon-based film.Alternatively, a silicon oxide film and a silicon nitride film areetched simultaneously.

(2) Damage to mask materials, such as ACL, Poly-Si, and SiON, and to lowdielectric constant materials, such as SiOC, caused by plasma etchingcan be reduced. Thus, impairment of device characteristics and reductionin yield can be prevented/suppressed.

In order to etch a silicon oxide film and/or a silicon nitride film withhigh selectivity relative to ACL, Poly-Si, SiON, or a carbon-containingsilicon-based film, it has heretofore been necessary to mix a pluralityof FC gases and/or HFC gases in accordance with the object to be etched,and control the mixing rate, etc. With the present invention, highlyselective etching of a silicon oxide film or a silicon nitride film isachieved by employing a specific hydrofluorocarbon alone or as anetching gas composition including O₂ and/or Ar.

During plasma etching employing this etching composition, hydrogen atomsincluded in the specific hydrofluorocarbon and excessive fluorineradicals in the plasma react with one another and are discharged as HF,and thus, the etching of silicon film (crystalline silicon, amorphoussilicon, polysilicon) can be prevented.

In a plasma using the specific hydrofluorocarbon etching gascomposition, positive ions having 3 to 5 carbon atoms and also includingfluorine atoms and hydrogen atoms, such as C₃FH⁺, C₃F₃H₂ ⁺, C₄F₄H₂ ⁺,and C₅F₅H₂ ⁺, are mainly produced; such ions are less likely to form areactive layer on carbon-rich ACL or on a carbon-containingsilicon-based film represented by SiC, SiOC, SiCN, SiOCN, or the like,and thus, etching is suppressed/prevented. In a silicon oxide film,etching proceeds because the oxygen in the silicon oxide film reactswith the carbon in the ions, to produce CO and CO₂. In a silicon nitridefilm, etching proceeds because the nitrogen in the silicon nitride filmreacts with the hydrogen and carbon in the ions, to produce HCN and NH₃.Further, a plasma using the specific hydrofluorocarbon etching gascomposition produces no CF₃ ⁺, which is present in a C₄F₆ plasma. Ingeneral, CF₃ ⁺ has a high etching rate but has low selectivity; thus, itis considered that a plasma using the specific hydrofluorocarbon etchinggas composition, in which no CF₃ ⁺ is produced, is suitable forselective etching.

In general, ions with a larger number of carbon atoms do not penetrateinto an object-to-be-etched as deeply as ions having a smaller number ofcarbon atoms when implanted with the same energy, and can thus beexpected to cause less damage to parts that are not to be etched, suchas an undercoat film for etching.

1. A gas composition for dry etching, comprising a hydrofluorocarbon gasthat has an unsaturated bond in its molecule and is represented byCxHyFz, wherein x is an integer of from 3 to 5, and relationships y+z≤2xand y≤z are satisfied.
 2. The gas composition for dry etching accordingto claim 1, wherein the hydrofluorocarbon gas comprises1,1,4,4-tetrafluoro-1,3-butadiene.
 3. The gas composition for dryetching according to claim 2, wherein the content of1,1,4,4-tetrafluoro-1,3-butadiene in the hydrofluorocarbon gas is from 1to 100 vol %.
 4. The gas composition for dry etching according to claim2, wherein the gas composition for dry etching includes, in addition to1,1,4,4-tetrafluoro-1,3-butadiene, at least one compound selected fromthe group of oxygen-atom-containing compounds consisting of O₂, O₃, CO,CO₂, NO, NO₂, SO₂, and SO₃.
 5. The gas composition for dry etchingaccording to claim 2, wherein the gas composition for dry etchingincludes, in addition to 1,1,4,4-tetrafluoro-1,3-butadiene, at least onecompound selected from the group of inert gases consisting of N₂, He,Ar, Ne, and Xe.
 6. A dry etching method comprising a selective etchingstep wherein a multilayer structure including (a1) a carbon-containingsilicon-based film, (a2) a crystalline silicon film, (a3) an amorphoussilicon film, (a4) a polycrystalline silicon film (polysilicon film),(a5) a silicon oxynitride film, or (a6) an amorphous carbon film, and(b1) a silicon oxide film or (b2) a silicon nitride film is subjected toplasma etching by using the gas composition for dry etching according toclaim 1, and thus selectively etching the silicon oxide film (b1) or thesilicon nitride film (b2).
 7. The dry etching method according to claim6, wherein etching with the gas composition for dry etching is performedunder a plasma condition in which the silicon oxide film (b1) and thesilicon nitride film (b2) can be etched simultaneously.
 8. The dryetching method according to claim 6, wherein etching of the siliconoxide film (b1) is performed selectively relative to the silicon nitridefilm (b2).
 9. The dry etching method according to claim 6, whereinetching is performed by turning the gas composition for dry etching intoplasma so that ions having 3 to 5 carbon atoms are produced.
 10. The gascomposition for dry etching according to claim 3, wherein the gascomposition for dry etching includes, in addition to1,1,4,4-tetrafluoro-1,3-butadiene, at least one compound selected fromthe group of oxygen-atom-containing compounds consisting of O₂, O₃, CO,CO₂, NO, NO₂, SO₂, and SO₃.
 11. The gas composition for dry etchingaccording to claim 3, wherein the gas composition for dry etchingincludes, in addition to 1,1,4,4-tetrafluoro-1,3-butadiene, at least onecompound selected from the group of inert gases consisting of N₂, He,Ar, Ne, and Xe.
 12. A dry etching method comprising a selective etchingstep wherein a multilayer structure including (a1) a carbon-containingsilicon-based film, (a2) a crystalline silicon film, (a3) an amorphoussilicon film, (a4) a polycrystalline silicon film (polysilicon film),(a5) a silicon oxynitride film, or (a6) an amorphous carbon film, and(b1) a silicon oxide film or (b2) a silicon nitride film is subjected toplasma etching by using the gas composition for dry etching according toclaim 2, and thus selectively etching the silicon oxide film (b1) or thesilicon nitride film (b2).
 13. A dry etching method comprising aselective etching step wherein a multilayer structure including (a1) acarbon-containing silicon-based film, (a2) a crystalline silicon film,(a3) an amorphous silicon film, (a4) a polycrystalline silicon film(polysilicon film), (a5) a silicon oxynitride film, or (a6) an amorphouscarbon film, and (b1) a silicon oxide film or (b2) a silicon nitridefilm is subjected to plasma etching by using the gas composition for dryetching according to claim 3, and thus selectively etching the siliconoxide film (b1) or the silicon nitride film (b2).
 14. A dry etchingmethod comprising a selective etching step wherein a multilayerstructure including (a1) a carbon-containing silicon-based film, (a2) acrystalline silicon film, (a3) an amorphous silicon film, (a4) apolycrystalline silicon film (polysilicon film), (a5) a siliconoxynitride film, or (a6) an amorphous carbon film, and (b1) a siliconoxide film or (b2) a silicon nitride film is subjected to plasma etchingby using the gas composition for dry etching according to claim 4, andthus selectively etching the silicon oxide film (b1) or the siliconnitride film (b2).
 15. A dry etching method comprising a selectiveetching step wherein a multilayer structure including (a1) acarbon-containing silicon-based film, (a2) a crystalline silicon film,(a3) an amorphous silicon film, (a4) a polycrystalline silicon film(polysilicon film), (a5) a silicon oxynitride film, or (a6) an amorphouscarbon film, and (b1) a silicon oxide film or (b2) a silicon nitridefilm is subjected to plasma etching by using the gas composition for dryetching according to claim 5, and thus selectively etching the siliconoxide film (b1) or the silicon nitride film (b2).
 16. The dry etchingmethod according to claim 7, wherein etching is performed by turning thegas composition for dry etching into plasma so that ions having 3 to 5carbon atoms are produced.
 17. The dry etching method according to claim8, wherein etching is performed by turning the gas composition for dryetching into plasma so that ions having 3 to 5 carbon atoms areproduced.
 18. A dry etching method comprising a selective etching stepwherein a multilayer structure including (a1) a carbon-containingsilicon-based film, (a2) a crystalline silicon film, (a3) an amorphoussilicon film, (a4) a polycrystalline silicon film (polysilicon film),(a5) a silicon oxynitride film, or (a6) an amorphous carbon film, and(b1) a silicon oxide film or (b2) a silicon nitride film is subjected toplasma etching by using the gas composition for dry etching according toclaim 10, and thus selectively etching the silicon oxide film (b1) orthe silicon nitride film (b2).
 19. A dry etching method comprising aselective etching step wherein a multilayer structure including (a1) acarbon-containing silicon-based film, (a2) a crystalline silicon film,(a3) an amorphous silicon film, (a4) a polycrystalline silicon film(polysilicon film), (a5) a silicon oxynitride film, or (a6) an amorphouscarbon film, and (b1) a silicon oxide film or (b2) a silicon nitridefilm is subjected to plasma etching by using the gas composition for dryetching according to claim 11, and thus selectively etching the siliconoxide film (b1) or the silicon nitride film (b2).
 20. The dry etchingmethod according to claim 19, wherein etching is performed by turningthe gas composition for dry etching into plasma so that ions having 3 to5 carbon atoms are produced.